Known finned tube heat exchangers include plate-shaped fins arranged at a predetermined fin interval and heat transfer pipes (hereinafter referred to as “flat pipes”) that have a flat shape having a larger width than height. Such finned tube heat exchangers including flat pipes are hereinafter referred to as “flat pipe heat exchangers”.
Compared with heat exchangers including circular pipes, a typical flat pipe heat exchanger can ensure a large area of heat transfer of the pipes and reduce the ventilation resistance of heat exchange fluid and thus provide improved heat transfer performance. In contrast, if the flat pipe heat exchanger is used as an evaporator, its drainage performance is inferior to that of the heat exchangers including circular pipes because water drops readily remain on the surfaces (flat surfaces) of the flat pipes due to their shape profile.
For example, if the flat pipe heat exchanger is used as a heat-source-side heat exchanger installed in an outdoor unit of an air-conditioning apparatus (exemplary refrigeration cycle apparatus), the water in the air (heat exchange fluid) condenses and forms frost on the heat-source-side heat exchanger during a heating operation. The frost formation leads to an increase in the ventilation resistance, impairment in the heat transfer performance, and damage to the heat exchanger. To avoid these problems, a typical air-conditioning apparatus has a defrosting operation mode. Undesirably, if water drops remain in the heat-source-side heat exchanger, the water drops refreeze and form a larger volume of frost. That is, the heat-source-side heat exchanger having low drainage performance requires a longer period of defrosting operation, resulting in impairment in comfortability and a reduction in average heating capacity.
To solve these problems, heat exchangers designed to improve the drainage performance have been developed (for example, refer to Patent Literature 1). Patent Literature 1 discloses “a fin-and-tube type heat exchanger comprising vertical flat-plate fins having notches and flat pipes inserted into side surfaces of the fins, wherein the flat pipes are inserted from a downstream side of an air flow, and the notches are provided in the fins such that sections of the flat pipes are angled upward with respect to the air flow.”